The use of drug dispensers in the administration of drugs, for example in bronchodilation therapy is well known. Such dispensers generally comprise a body or housing within which a drug carrier is located. A known drug dispenser has a drug carrier in the form of an elongate blister strip containing a number of discrete doses of drug in powder or tablet form. The elongate blister strip comprises a base sheet having pockets defined therein and a lid sheet provided thereto, wherein the base sheet and lid sheet are peelably separable to allow access to the contents of each pocket. The lid sheet and base sheet typically comprise laminated foil materials. Such dispensers typically contain a mechanism of sequentially accessing the dose-containing pockets, for example comprising peeling means for peeling the lid sheet away from the base sheet. The drug is thereby made available for delivery to the patient.
Suitable peeling means are positioned to peel apart a base sheet and a lid sheet of a pocket at an opening station of the dispenser. The peeling means typically includes a (lid or base) sheet driver for pulling apart a lid sheet from a base sheet of a pocket that has been received at the opening station. In one embodiment, the sheet driving means comprises a fixed-diameter wheel on which the (e.g. lid) sheet is wound, the wheel having an effective winding surface, the diameter of which increases as more (e.g. lid) sheet is wound about said wheel.
A problem encountered with the use of such a fixed-diameter wheel as the sheet driver for driving a sheet of a drug carrier is that as the sheet winds up around the wheel the effective winding diameter of the wheel increases, and therefore its effective lateral pulling action (i.e. length of pull) also increases. This is problematic because it is desirable that on actuation, a definable pull action is experienced by the drug carrier pocket at the opening station to ensure that a generally uniform indexing/opening effect is experienced by each pocket of the drug carrier. In general terms, insufficient pull action will result in failure to open up the pocket whilst excess pull will put stress on the mechanical components and increase the force required to actuate the dispenser.
A solution to the above problem has been described in Applicant's PCT Patent Application No. WO-A-2006/018261 and counterpart U.S. Ser. No. 11/573,656, the disclosures of which are incorporated herein by reference. Therein is described a (lid or base) sheet driver having the form of a hub incorporating compensating means in the form of a central shaft-mounted torsion spring to compensation for the increase in effective winding diameter.
Another problem that can potentially be encountered is that a sheet (i.e. lid sheet or base sheet) of the elongate blister strip may become damaged during use, for example as a result of tearing, stretching or de-lamination thereof. A reduction (or complete lack) of ‘sheet pulling force’ is thereby, experienced at the (lid or base) sheet driver, which impairs or prevents the ability of the sheet driver to correctly wind up the sheet thereon. As a result, the pockets containing drug are also not advanced correctly and/or are not peelably opened fully or at all by the pocket opening mechanism of the dispenser. The ability of the drug dispenser to make drug available for delivery to the patient is therefore either substantially impaired or entirely prevented, which ‘failure’ can have serious consequences for the patient. The ‘failure’ can be compounded where the patient does not realize that the strip advancement and/or pocket opening mechanism of the drug dispenser has been impaired, and the patient continues to use the dispenser unaware that drug delivery is not happening correctly or at all. It is thus, desirable to provide a clear indication to the patient of the ‘failure’ of the dispenser.
In solution, the Applicant has devised a sheet driver that includes an indicator pin that ‘pops out’ when loss of pulling force (as would normally be applied by an undamaged sheet) is experienced at the sheet driver. In a development of the solution, the indicator pin can be made to engage in locking fashion one or more elements of the drug dispenser when in its ‘popped out’ position, thereby preventing any further use of the dispenser. The patient is thereby, given a very clear message that the dispenser has ‘failed’ and that a replacement must be obtained. More generally, the Applicant has devised a spool for winding up a tape which is provided with a fault indicator to indicate a fault with the tape.
Applicant's co-pending PCT Patent Application No. WO-A-2006/123110, the disclosure of which is incorporated herein by reference, describes a fault indicator mechanism for use with a drug dispenser in which an elongate blister strip is advanced to various blister opening positions.